This invention relates to a simple stepless variable transmission.
There has been a long felt but unmet need for an efficient, durable and mechanically simple stepless variable transmission, as evidenced by the number of prior inventions related to the subject. Many machines, based on a variety of principles, have been proposed or built in an effort to achieve these goals, yet to date there has not been a truly successful simple stepless variable transmission.
U.S. Pat. No. 1,257,479 to Grant discloses a transmission mechanism providing for multiple partial rotations of a tubular shaft and disks that can be moved from concentric to eccentric positions. The disks also have yokes, cams and racks.
U.S. Pat. No. 2,254,195 to Cicin discloses a stepless mechanical torque converter that converts rotations into turning motions, linear reciprocating movements, rotating oscillations and into uniform rotation.
U.S. Pat. No. 2,691,896 to Stageberg discloses a variable speed power transmission using a crank mechanism that includes a plurality of connecting rods and ratchet mechanisms.
U.S. Pat. No. 3,448,627 to Brooks discloses a gearless variable drive mechanism utilizing a rotating disk with an eccentric groove, a plurality of one way clutches and circumferentially spaced members engaging each of the clutches and the eccentric groove, each of the clutches having cam surfaces.
U.S. Pat. No. 3,881,362 to Beezer discloses a device for transmitting controlled movements in both an X axis and a Y axis direction including a rotatable shaft with separate drive cams for separately driving levers connected through slides to a first member which is guided for movement in an X direction and also connected through a cam drive and an adjustable slide to a second member which is mounted for movement along the Y axis.
U.S. Pat. No. 3,924,478 to Takasu discloses a speed reduction mechanism utilizing an eccentric with a driving disk mounted freely for rotation on the eccentric.
U.S Pat. No. 4,112,778 to Korosue discloses a variable speed power transmission provided with rotary units that are mounted on an input axis and an output axis and parallel with each other with a phase angle difference between the rotary units, each of the rotary units having eccentric cams and a clutch.
U.S. Pat. No. 4,411,172 to DeMarco discloses a variable speed reducing and torque transmitting mechanism including a pair of counter rotating low speed impellers being driven from a spider shaft rotating at relatively high speed.
U.S. Pat. No. 4,493,222 to Heine discloses a gearless speed and torque converter using an input member mounted on a rotatable input shaft that has an Archimedes spiral groove bearing surface with an adjacently exposed output member with a complementary Archimedes spiral groove bearing surface where the grooves have different pitches. The shafts are coaxially mounted and a plurality of balls are disposed between the respective spiral grooves.
U.S. Pat. No. 4,765,195 to Takami discloses a stepless transmission mechanism ;sing intermeshing noncircular gears and multiple shafts.
Traction machines have shown some success in light duty applications but have failed in heavy duty service. Torque converters have been used in more demanding situations but with considerable loss of efficiency. Purely mechanical, modified motion mechanisms have suffered either from complexity of design or from lack of smooth motion at the output shaft, resulting in limited and specialized applications.
The basic approach to purely mechanical, non-friction type stepless transmissions utilizing cams, linkages, noncircular gears and other members is, first, to use an input to drive a plurality of intermediate stages through cycles phased appropriately with the input. A selector mechanism then extracts and recombines the desired portion of the driven cycle of each of the parallel intermediate stages to drive the output shaft, usually through one way (overrunning) clutches and/or differentials (Takami, Brooks, Korosue, Stageberg). Other types of more complicated coupling through timed gear engagement can be found (Grant), as well as yet more complicated arrangements with conversion of rotary motion to linear and back to rotary (Cicin).
A key characteristic of prior stepless variable transmissions is the required plurality of parallel intermediate modules. Each parallel module creates a full cycle of a periodic motion for each revolution of the input shaft, subsequently transferring a portion of that motion to the output shaft (FIG. 8). The general shortcoming of these devices is that, at the transition point, when the driving force switches from one intermediate module to the next, there is an abrupt change in the magnitude and direction of the velocity and/or accelerating force reflected on the output shaft. In most cases (Brooks, Korosue, Stageberg) there also exists a large difference between the maximum and minimum velocity of each module during the power portion of the cycle (FIG. 5), which is transmitted to the output shaft. The end result is that the output shaft motion is the summation of a series of impulses, usually smoothed out only by drive line inertia. The final result is that the impulses produce shock loads requiring oversize components even in light duty applications. There are instances where force and velocity discontinuities are not carried in the power portion of the mechanism (Takami's angular velocity modulation mechanism). Nevertheless, there is shock loading in the transition of the drive components from one exponential ratio to another, a weakness inherent in the design if the number of parallel intermediate stages is to be minimized.
It is therefore an objective of this invention to achieve stepless rotational speed variation between an input shaft and an output shaft with high mechanical efficiency and a minimum of intermediate modules.
It is another objective of this invention to produce smooth motion at the output shaft, eliminating step changes in velocity and in acceleration of moving parts, thereby eliminating shock loads on the transmission components.
It is yet a further objective of this invention to achieve stepless speed variation by using a very small number of easily fabricated parts, capable of competing commercially with existing multiple fixed ratio speed variators.
It is yet a further objective of this invention to achieve stepless speed variation of high accuracy with minimum added mechanical complexity.
It is yet another objective to provide a simple means of controlling the steplessly variable mechanism, capable of easily interfacing with existing automatic control schemes, to produce an automatic stepless variable transmission.